I would say its the fact that DX10.1 has global lighting enabled; this makes the game coding more streamlined (as in they don't have to manually program each object to be affected by a lighting source-afaik it would probably put an increased load on the GPU itself).
AMD Radeon X1950~HD4000 Support Clubhouse
“Mac: "Woah, what are you doing?" Mac says as he levitates in the air.
PC: "Playing Half-Life 2, this is my gravity gun."
Mac: "Well I can sort of do that."
PC: "Technically Mac, you have to become me first."” -From_Nowhere